Charge Heterogeneity and Surface Chemistry in Polycrystalline Cathode Materials

Abstract

Abstract:Nanoscale full-field (FF) transmission X-ray microscopy (TXM) and ensembleaveraged soft X-ray absorption spectroscopy (soft XAS) were used to investigate stateof-charge (SOC) heterogeneities in electrochemically charged or discharged and chemically oxidized samples of LiNi0.6Mn0.2Co0.2O2 cathode materials. We observed considerable and similar non-uniformities in terms of Ni oxidation states (and, by proxy, lithium distributions) for all the samples in the bulk. Therefore, the chemically delithiated samples are similar to the electrochemically charged samples in terms of mesoscale charge heterogeneity in large polycrystalline particle ensembles. However, the gradient oxidation states of transition metals on the surface, which is partly responsible for the electrode degradation mechanism known as surface reconstruction, is much less apparent in chemically delithiated samples. T Response to ReviewersThe previous version of this paper was not sent out for peer review. Response to Reviewers Graphical AbstractClick here to download Graphical Abstract graphicalabstract.tif Charge Heterogeneity and Surface Chemistry in Polycrystalline Cathode Materials SummaryNanoscale full-field (FF) transmission X-ray microscopy (TXM) and ensemble-averaged soft Xray absorption spectroscopy (soft XAS) were used to investigate state-of-charge (SOC) heterogeneities in electrochemically charged or discharged and chemically oxidized samples of LiNi0.6Mn0.2Co0.2O2 cathode materials. We observed considerable and similar non-uniformities in terms of Ni oxidation states (and, by proxy, lithium distributions) for all the samples in the bulk. Therefore, the chemically delithiated samples are similar to the electrochemically charged samples in terms of mesoscale charge heterogeneity in large polycrystalline particle ensembles.However, the gradient oxidation states of transition metals on the surface, which is partly responsible for the electrode degradation mechanism known as surface reconstruction, is much less apparent in chemically delithiated samples.

Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na

“…Since Na occupies Li site, the gradient Na distribution demonstrates that the deintercalation of Li‐ion is also in a gradient feature. Namely, more Li‐ions are extracted out from surface layers, which is consistent with the previous AFM and TXM observations . It may argue that Na depletion in the core region is not due to less Li vacancies but poor accessibility to Na source.…”

Faster Activation and Slower Capacity/Voltage Fading: A Bifunctional Urea Treatment on Lithium‐Rich Cathode Materials

“…The Ni L‐edge spectra are shown in Figure S11 (Supporting Information), the spectra correspond to transitions from Ni 2p to Ni 3d, split by the spin–orbit interaction of the Ni 2p core level. The evolution Ni oxidation state can be investigated by observing the change in peak located at ≈854 and ≈870 eV 29,34. During the cycling, the position of these peaks for both LMR and LMR‐U are nearly unchanged, suggesting no significant evolution of Ni valence.…”

Radially Oriented Single‐Crystal Primary Nanosheets Enable Ultrahigh Rate and Cycling Properties of LiNi0.8Co0.1Mn0.1O2 Cathode Material for Lithium‐Ion Batteries

“…Formation of cracks is inhibited by the unique crystallographic texture of radially aligned single-crystal primary particles, despite the fixed anisotropic lattice variation accompanied by the Li + insertion/extraction. Besides, the enhanced Li + diffusion coefficient and electronic conductivity of RASC-NCM material are beneficial to homogenizing the state of charge (SOC) on the particle level, [28,29] reducing the possibility of over delithiation at the particle surface. This improved mechanical stabilization prevents the infiltration of electrolyte and the formation of damaged surface layers.…”